The present invention relates to a commutator.
A commutator for a DC motor includes a cylindrical insulator fixed to a rotary shaft of an armature, and multiple conductive segments attached to the outer circumferential surface of the insulator. Each segment has a riser connected to an end of a coil wound around a core of the armature. Feeding brushes are in sliding contact with the outer circumferential surfaces of the segments. The feeding brushes feed a direct current to the coil of the armature via the segments.
The aforementioned commutator is manufactured as follows. A cylindrical conductive material is placed in a die and a plastic material is poured into the cylindrical material, thereby forming the aforementioned insulator. Then, the cylindrical material is cut along the axis to form the aforementioned segments.
Japanese Laid-Open Patent Publication No. 2002-51506 discloses such a commutator. According to Japanese Laid-Open Patent Publication No. 2002-51506, in order to ensure force of engagement between the insulator and each segment, a surface of the segment contacting the insulator is roughened by being dipped in a roughening liquid to become a roughened surface of a structure with tiny recesses and projections. This roughened surface increases the area of engagement between the segment and the insulator, compared to the case where the aforementioned surface of the segment is smooth without a structure with recesses and projections, thereby increasing the force of engagement there between.
The aforementioned segment of the commutator should be subjected to aftertreatment after formation of the roughened surface, such as removal of the roughening liquid existing on the roughened surface. In the absence of this aftertreatment, the roughened surface is continuously roughened. This changes the structure with recesses and projections for example, leading to reduction of the force of engagement between the segment and the insulator. Hence, manufacture of the commutator involves a large number of steps.